The long term goal of this project is to improve our understanding of how neural systems in the human brain subserve aversive emotional states like fear and anxiety by assessing the brain metabolic activity of healthy volunteers with Functional Magnetic Resonance Imaging (fMRI). Specifically, this project will focus on the acquisition and performance of Pavlovian fear conditioning by assessing dynamic changes in regional activation during the learning process and when a fear response is expressed. These goals will be achieved with two experiments. In the first experiment, volunteers will be initially trained (acquisition) to fear a neutral stimulus. Then their memory for the previous training (performance) will be assessed. Functional and anatomical images will be obtained during both acquisition and performance phase. In the second experiment, volunteers will be differentially trained to fear one stimulus (Csplus) and not to fear a second stimulus (CS-). In this experiment, subjects will serve as their own control, and Probe trials will be used to make comparisons without UCS presentation. These experiments will answer questions about which neural structures are involved in learning and expression of conditional fear, will describe the temporal pattern of activation within these structures, will provide insights into how the involvement of various structures change as learning occurs and fear is expressed, and will comparisons with learning animal model systems. The data to be collected will substantially advance our understanding of neuroanatomical mechanisms of human fear and anxiety, and may directly contribute to improvements in the assessment and treatment of affective disorders.